Thioredoxin, a small dithiol protein, is a specific reductant for major food proteins, allergenic proteins and particularly allergenic proteins present in widely used foods from animal and plant sources. Most proteins having disulfide (S—S) bonds are reduced to the sulfhydryl (SH) level by thioredoxin. These proteins are allergenically active and less digestible in the oxidized (S—S) state. When reduced (SH state), they lose their allergenicity and/or become more digestible. Of importance is the thioredoxin reduction of disulfide bonds in proteins such as albumins, globulins, gliadins, thionins, and the glutenins found in many seeds and cereals, and also a number of proteins found in milk. See, for example, Kiss, F. et al. (1991), Arch. Biochem. Biophys. 287:337–340; Johnson, T. C. et al. (1987), Plant Physiol. 85:446–451; Kasarda D. D. et al. (1976), Adv. Cer. Sci. Tech. 1:158–236; and Osborne T. B. et al. (1893), Amer. Chem. J. 15:392–471; Shewry, P. R. et al. (1985), Adv. Cer. Sci. Tech. 7:1–83; Dahle, L. K. et al. (1966), Cereal Chem. 43:682–688; Garcia-Olmedo, F. et al. (1987), Oxford Surveys of Plant Molecular and Cell Biology 4:275–335; Birk, Y. (1976), Meth. Enzymol. 45:695–739, and Laskowski, M., Jr. et al. (1980), Ann. Reo. Biochem. 49:593–626; Weselake, R. J. et al. (1983), Plant Physiol. 72:809–812; Birk, Y. (1985), Int. J. Peptide Protein Res. 25:113–131, and Birk, Y. (1976), Meth. Enzymol. 45:695–739; Birk, Y. (1985), Int. J. Peptide Protein Res. 25:113–131.
In addition, thioredoxin reduces the disulfide bonds in many toxic proteins, such as those found in snakes (Yang, C. C. (1967) Biochim. Biophys. Acta. 133:346–355; Howard, B. D. et al. (1977) Biochemistry 16:122–125), bees, scorpions (Watt, D. D. et al. (1972) Toxicon 10:173–181), the bacterial neurotoxins tetanus and botulinum (Schiavo, G. et al. (1990) Infection and Immunity 58:4136–4141; Kistner, A. et al. (1992) Naunyn-Schmiedeberg's Arch Pharmacol 345:227–234), and thereby reduces or in some instances eliminates their toxicity altogether.
Thioredoxin achieves this reduction when activated (reduced) either by nicotinamide adenine dinucleotide phosphate (NADPH) via NADP-thioredoxin reductase (physiological conditions) or by dithiothreitol, a chemical reductant. See, for example, U.S. Pat. No. 5,952,034, incorporated herein by references in its entirety. Skin tests and feeding experiments carried out with sensitized dogs have shown that treatment of the food with reduced thioredoxin prior to ingestion eliminates or decreases the allergenicity of the food. Studies have also shown increased digestion of food and food proteins by pepsin and trypsin following reduction by thioredoxin.
Thus, it would be deirable to develop an efficient, low cost method of using thioredoxin reductase to reduce the toxicity of toxic proteins, reduce the allergenicty of food, and increase the digestibility of food.